MTA Service Bump Next June Won’t Keep Up With Growth in Subway Trips

Talk about running in place: At current growth rates in subway ridership, the service increases that NYC Transit is promising to roll out next June will probably be used up by April.

That doesn’t mean the increases are a bad idea, of course. Rather, it underscores the need for transformational increases in subway capacity, rather than incremental moves like the bump announced by the MTA last Friday.

Here’s the deal: Annual subway ridership increased every year from 2009 to 2014. (Data for 2015 aren’t in yet.) The 11 percent rise, to 1.75 billion trips last year from 1.58 billion in 2009, works out to an annual average increase of 2.1 percent. There are now 6 million subway trips on a good weekday, with some 90 percent of those trips, or 5.4 million, happening between 6 a.m. and 7 p.m. Just a single year’s growth, at 2.1 percent, amounts to 113,000 rides during that 15-hour peak.

By comparison, the 36 additional trains that NYC Transit intends to run on weekdays — 10 on the 1/2 line, six on the A/C/E, six on the J/M/Z, and 14 on the 4/5/6 — will add room for 45,900 additional passengers (multiplying 36 trains by 10 cars per train by 127.5 riders per car). Throw in 5,000 to 10,000 more spaces for the greater frequency promised on the 42nd Street Shuttle, and the total gain in capacity reaches 55,000 — enough to handle a mere six months’ worth of ridership growth.

The takeaway is that enhanced service commitments like last Friday’s will be needed much more frequently. The only way that will happen is through transformational change, like implementing Communications-Based Train Control (CBTC) on every line.

CBTC supplants the century-old analog “fixed block wayside signal” system for monitoring and controlling train movements. In its place will be fiber-optic communications that link tracks and vehicles into a seamless system, as the Regional Plan Association summed it up in its comprehensive report on CBTC earlier this year. In a nutshell, where subways currently run at 20-25 trains per hour, CBTC would allow at least 30.

If that could be done across the system, a simple calculation — 14 lines (I exclude the L, which was already upgraded to CBTC) times 7.5 more trains per hour times 15 hours per day times 1,275 additional passenger capacity per train — suggests an increased capacity of 2 million passengers per day. That means subways could carry at least one-third more passengers than the estimated 5.4 million riders now traveling between 6 a.m. and 7 p.m., when the trains are most crowded. Or some of the new capacity could alleviate crowding, not only making subway travel more humane but reducing delays caused by crowding itself as passengers struggle to enter and exit packed trains and stations.

The calculation here doesn’t address logistical concerns, not to mention costs of buying, staffing, servicing and running the increased trains. But it underscores the vast potential and need to begin bringing subway infrastructure into the 21st Century now — a process that will require full funding of not just the current MTA capital plan but future five-year plans as well.

I’m pretty sure there are short overlaps all over the system because that’s the way the signal system was originally designed. What makes you think “it’s only a small percentage of signals on some lines”? Do you know something I don’t (which is very possible)?

Brian Howald

I’ve experienced both of those, as well as 63rd Drive w/b. I don’t know why these timers are there, but given as they restrict trains moving when the line is relatively empty, I figure they aren’t there to space trains, and won’t be obviated by CBTC.

The Joralemon, Clark, and Cranberry St. tubes all have a decent curve in them, but even the Steinway tubes, which (except for that kink e/b) do not, have timers on the downgrades. The 60th Street tunnels do not, and the difference is felt. Heading south towards Chambers St on the 7th Avenue line, the express track has timers, but the local does not, even with roughly similar track geometry. I’m really can’t see the rhyme or reason behind many of NYCTA’s timers.

Joe R.

The issue is due to three factors. One is instances where the signals are spaced more closely than usual. Sometimes this is done to increase track capacity. Other times it’s just a vestige of an era when equipment performance was lower, hence the older trains couldn’t reach speeds exceeding the limits of the signal system but the new ones can. The latter would actually be mostly a problem on the IRT. Most of the IND was built post WWII, when trains were only marginally slower, or the same as now. Also, the IND was built with faster running in mind compared to the IRT, so signals were spaced further apart. In any case, there aren’t that many places where the signals are problem. Remember until the WB collision we were running unneutered trains system wide without any issues. If there were so many places where the signal system was flawed, we would have had a lot more collisions.

The second cause when trains were overhauled in the late 1980s through early 1990s. 100 HP motors were replaced with 115 HP motors. This increased the acceleration capabilities of the trains slightly. In most cases the signal system could still cope with it because signal systems have margins of safety built in. In a few instances, like on the WB, it couldn’t.

The third cause was changing the composition of the brake shoes. This reduced emergency braking capabilities slightly.

In the end, it was the unhappy collision of all three factors at the same time which resulted in the WB accident. Could such a thing happen in other parts of the system? Certainly it could. However, a proper solution might have been to see where the problems were, then if need be install timers to limit train speeds only in those areas. Still not an ideal solution, but at least you would only have a slowdown in a fraction of the system, not everywhere.

Boris

It is true that today high-rise residential offers a greater return, but is it the job of the city to always encourage what benefits developers the most? Or should it encourage what benefits residents? I’m not against more residential in the city, although I think the burden of growth should be more spread out, and not concentrated in high-rises in a few neighborhoods.

Mixed-use commercial or manufacturing could be a long-term play: the kind of thing the EDC should be doing. After 20 years of giving tax breaks to suburban mall developers, stadiums, and parking garages, they can instead incentivize middle class jobs in transit-oriented developments.

Joe R.

Grade timers operate 24/7. The MTA doesn’t really have the option to turn them off when there aren’t many trains.

I’m really can’t see the rhyme or reason behind many of NYCTA’s timers.

Neither can I which is why I’m complaining about them. If they were only installed in places where the trains really need to slow for curves, then that’s fine. This doesn’t seem to be the case. Also, as I mentioned elsewhere, these timers often force trains into the range of speeds where there is greater oscillation, increasing track wear, plus detracting from passenger comfort. They largely make no sense. No other system uses them to the extent the MTA does.

Joe R.

It’s probably a balancing act given that developer’s interests in maximizing profit are counter to the concept of affordable housing.

I agree wholeheartedly with the concept of spreading new development everywhere. However, to do that we’ll eventually need to build a lot more subways in the outer boroughs. Downtown Flushing is a great example of what the roads end up like if you develop without providing adequate mass transit.

NYC can and should attract a lot more commercial and manufacturing. Gone are the days when most manufacturing means heavy pollution or other negatives. Lots of things you could put right in NYC like major electronics manufacturing, research labs, etc. It’s an irony that NYC turns out some of the best science and engineering graduates but that many must face a choice of staying in the city underemployed, or relocating to work in a sterile suburban campus type environment (and driving to work). It doesn’t need to be that way.

fdtutf

One is instances where the signals are spaced more closely than usual. Sometimes this is done to increase track capacity.

It has never been the practice to space signals more closely than is safe. So that’s not really a factor.

Other times it’s just a vestige of an era when equipment performance was lower, hence the older trains couldn’t reach speeds exceeding the limits of the signal system but the new ones can.

This is the main issue.

The latter would actually be mostly a problem on the IRT. Most of the IND was built post WWII, when trains were only marginally slower, or the same as now. Also, the IND was built with faster running in mind compared to the IRT, so signals were spaced further apart.

Your discussion here omits the BMT, on which the 1995 collision occurred. In terms of signal overlap planning and standards, the BMT probably more closely resembles the IRT.

In any case, there aren’t that many places where the signals are problem.

How do you know this, I ask again?

Remember until the WB collision we were running unneutered trains system wide without any issues. If there were so many places where the signal system was flawed, we would have had a lot more collisions.

Of course that isn’t necessarily true, because the other barriers that are in place to prevent collisions (procedures, employee training, etc.) are often effective even when the signal systems may not be 100% effective.

The second cause when trains were overhauled in the late 1980s through early 1990s. 100 HP motors were replaced with 115 HP motors. This increased the acceleration capabilities of the trains slightly. In most cases the signal system could still cope with it because signal systems have margins of safety built in. In a few instances, like on the WB, it couldn’t.

“In most cases”? What’s your source for this?

In the end, it was the unhappy collision of all three factors at the same time which resulted in the WB accident. Could such a things happen in other parts of the system? Certainly it could. However, a proper solution might have been to see where the problems were, then if need be install timers to limit train speeds only in those areas. Still not an ideal solution, but at least you would only have a slowdown in a fraction of the system, not everywhere.

I think there may be many more portions of the system where this is a potential problem than you are willing to acknowledge.

I don’t like the fact that the trains are so much slower today than they used to be, but I applaud the MTA for putting safety ahead of speed.

Joe R.

My “source” is the fact the MTA ran the post-GOH trains for a number of years without incident until the WB collision in 1996. It’s sort of like the same “source” I use when I say passing red lights on a bike is safe. I use the fact that this practice has been safely done by thousands of riders for many years as proof that it’s safe. It’s no different here. Had a problem existed in some large portion of the signal system it would have been noticed as soon as the MTA started running faster trains. Operator training wouldn’t have prevented it because TOs aren’t trained to hold back when they have a clear aspect (RR parlance for a green light) in front of them. To the best of my knowledge no railroad employees are. Clear means proceed at either maximum track speed, or maximum equipment speed, whichever is less.

I don’t know exactly how many problem signals exist, but I do know in general it’s common practice to have a large margin of safety when spacing signals. It wasn’t that most of the signals were barely adequate for the older, slower trains. Rather, it’s that most had such huge margins that there was still a margin for error even with the newer, faster trains. In the few cases where this wasn’t true, it wasn’t because the signals were spaced more closely than is safe. Rather, they were spaced such that the margin of safety when using older equipment was less, but still there. In a few rare cases, this spacing was now inadequate for modern equipment. I can’t really blame the MTA for that but I can blame them for not fixing the problem as quickly as possible. Certainly 19 years is more than enough time to have done this.

Operator training wouldn’t have prevented it because TOs aren’t trained to hold back when they have a clear aspect (RR parlance for a green light) in front of them.

(1) I know what an aspect is (I even know the difference between an aspect and an indication), but thanks.

(2) Since the problem that caused the 1995 (not 1996) crash only manifests itself when a train passes a red signal and is tripped (and the signal overlap is insufficient to protect a train stopped in the next block), how T/Os behave in response to a clear aspect is not relevant.

In the few cases where this wasn’t true, it wasn’t because the signals were spaced more closely than is safe. Rather, they were spaced such that the margin of safety when using older equipment was less, but still there.

Correct.

In a few rare cases, this spacing was now inadequate for modern equipment.

What I’m asking for a source on is your assertion that this is only “a few rare cases.” Your argument from indirect evidence doesn’t establish that.

Komanoff

Yes, off-peak ridership appears to have increased more rapidly than peak. But I’m not sure the difference is huge. I’ve just calculated the “Gini Coefficient” — a measure of peakiness (vs. flatness) in a distribution (originally developed to characterize economic inequality, as you know) — for 2012 subway trips to and from the CBD, and same for 2007. The coefficient fell (indicating greater flatness), but only by 1.5% — from 0.4433 for 2007, to 0.4365 for 2012. That’s noteworthy but not huge.

My source for 7.5 more trains an hour is the RPA report I linked to in my sixth graf.

Perhaps my estimate of a one-third increase in capacity from system-wide CBTC overstated the case. At least I’ve taken a stab at it. I’m convinced that unless we can “concretize” the value of funding this and future MTA capital plans, we’re going to end up with precious little.

Joe R.

There are a few articles on the subject but no sources of all the potential problem signals:

One of the articles mentions rewiring the signals to effectively add another block to the stopping distance:

“In some cases, officials say, correcting the problem may just be a matter of rewiring the signal. For instance, in the Williamsburg Bridge crash, the signal system sensed the presence of the stopped M train and turned the light behind it red, and the light behind that one yellow. The signals could be rewired so that both lights were red, which would have doubled the stopping room for the oncoming J train.”

This would have been the more sensible solution in that it would have attacked the source of the problem, namely the fact that in some cases the trains couldn’t stop in time to avoid a collision if they passed a stop aspect. The potential downside here might be to lower the maximum track capacity. However, my understanding here is in much of the system the capacity is limited by how fast you can turn trains at terminals, not by the signaling system.

Since the problem that caused the 1995 (not 1996) crash only manifests itself when a train passes a red signal and is tripped (and the signal overlap is insufficient to protect a train stopped in the next block), how T/Os behave in response to a clear aspect is not relevant.

Indirectly it is. The problem is the trains are capable in some cases of going too fast to stop in the required amount of space if they pass a stop signal. That in turn is caused by T/Os keeping the throttle wide open in response to a clear signal. The open question is how much of the system has this problem. My educated guess is only a relatively small portion but in any case I’m reasonably sure such information wouldn’t be made public. In practice this problem would only manifest itself when trains were running close to the capacity of the signal system, hence only a few blocks apart. This only occurs during peak periods. During those times for various reasons trains often don’t reach maximum speeds anyway. Maybe a simple rule like 35 mph maximum through problem areas during peak times might have solved the issue.

Joe R.

A second possible solution is to spread out the load through more of the day by giving employers incentives to allow employees to keep something other than 8 to 4 or 9 to 5 hours (also give incentives for 3 or 4 longer days instead of 5 8-hour days). Furthermore, incentives can be given for telecommuting. The idea to attack this on the demand side, rather than the supply side, makes more sense to me. It’s very expensive to add subway capacity. However, right now we have a lot of potential capacity off-peak which can be had for little cost. That and decreasing the number of trips via either telecommuting, or 3 or 4 day work weeks, seem like eminently sensible ideas.

ahwr

My question was why did capacity seem to go down? If the 32 tph capacity was based on short turning trains are you sure all 24 tph they were running went to 8th avenue?

ahwr

Just a single year’s growth, at 2.1 percent, amounts to 113,000 rides during that 15-hour peak.
…
total gain in capacity reaches 55,000 — enough to handle a mere six months’ worth of ridership growth.

Isn’t this only true if all the increase is at the peak load point? I assume the MTA has data on peak loading throughout the day for each line, would they care to share it?

sbauman

I’m quite certain that the only Manhattan terminal was 8th Ave.

fdtutf

The potential downside here might be to lower the maximum track capacity. However, my understanding here is in much of the system the capacity is limited by how fast you can turn trains at terminals, not by the signaling system.

That’s currently true precisely because the signaling system along the intermediate stretches does not limit capacity. If it were rewired to do so — itself an undertaking that is fraught with danger — there’s a good chance it would become a major limiting factor as well.

Indirectly it is. The problem is the trains are capable in some cases of going too fast to stop in the required amount of space if they pass a stop signal. That in turn is caused by T/Os keeping the throttle wide open in response to a clear signal.

To the extent that that may be a problem, that is a signal sighting issue that requires correction in any case. A T/O should always, always, always be able to see a red signal in time to stop without passing it; if that’s not the case, that’s a severe defect.

Here’s another article which mentioned 650 problem areas:

Are you trying to tell me that “650 problem areas” equals only a “small” part of the system?

However, with those speed limits in effect, why the need to neuter equipment such that it kills both acceleration and top speed?

They don’t trust T/Os.

Joe R.

On the 650 problem areas, it depends where they’re located. It might be that 400 of them are located after a curve or a station, or perhaps when entering a terminal. In theory the signal system would be inadequate to stop a train at maximum speed passing a red signal. In practice it would never happen because the train would never be going at maximum speed in that location. Also, there might be a lot of clustering of these problem areas, such that most of the track miles of the system don’t have a problem. Without more detail it’s impossible to say if 650 is a big problem or a small problem in terms of the total system. If distributed evenly over the system, this would translate to roughly 1 problem per track mile. Chances are great the majority of problems are concentrated on a few lines. I also wonder how many are just problems only in theory as I mentioned above?

The primary issue here is that this is only a problem when/if a T/O runs a red light. As such, you need a highly unlikely set of circumstances for the problem to manifest itself. That’s probably why it took years for a collision to happen despite there being 650 problem areas.

I’m holding to my position that the MTA overreacted here. Some corrective measures, like speed limits, or perhaps modifying the signal system in the problem areas, were certainly necessary. Wholesale slowing down of the entire system wasn’t. As for rewiring signals being fraught with danger, can’t the same be said about modifying the signaling system by adding more and more timers? Yet the MTA seemingly has no problem with the latter.

They don’t trust T/Os.

Then either you need new management or new T/Os. Every other rail system in existence largely trusts the operators to make decisions about speed. If the MTA wants to micromanage to this extent, then perhaps they should just get rid of the T/Os altogether as we convert to CBTC. Also, as a member of the riding public I vehemently object to paying T/Os what we pay them if the MTA considers them so low-skilled as to be incapable of obeying speed limits or signals. If that’s the case, pay minimum wage and hire anyone with a pulse to run trains.

I’m really curious why the TWU never stepped in to object to these ridiculous practices. Had I been on the job, I would have filed a grievance the second they neutered the trains. Micromanagement is fine when dealing with low-skilled labor right off the streets. T/Os take years to learn their craft. It’s an insult for the MTA to treat them like trained monkeys.

Alexander Vucelic

You forgot the Part about the consultant being the commisioner’s Son-in-law 🙂

Alexander Vucelic

certainly

Andrew

The facts are: there are many hours on many lines when trains can’t accommodate 100 percent of people who want to board

(Note that even 100% in this table is far short of a crush load. Not that loading in excess of 100% is desirable, but even at that undesirable point it’s not true that trains can’t accommodate those who want to board.)

People clog up in the door area long before the middle of the car fills up. Ask your fellow riders to move in.

Andrew

Let’s try to understand what CBTC is. It’s an acronym that stands for: Communication Based Train Control. The “Train Control” portion means collision and near miss avoidance. Any train control system needs to know the position of all trains on the rail.

Conventional block systems do this by dividing the track into a series of block s. A train passing on rails causes a short circuit between the rails that is detected by the train control system.

CBTC uses a different method to locate trains. Equipment on the train has an independent way of determining its position. The train then communicates its position to the train control system.

That’s the entire difference between CBTC and block systems: how the train is located. The train control system then uses this information to stop or control train speed to avoid collisions or near misses.

You’ve glossed over two important differences between fixed block and CBTC systems, as least as far as they exist on the subway.

First, by its very nature, the precision on a fixed block system is quite coarse. The signal system knows whether a block is occupied, but it has no way of knowing which part of the block is occupied. To be safe, it assumes the worst case, but that costs capacity.

Second, at least on the subway system, CBTC calculates and dictates the maximum speed on a continuous scale, based not only on track geometry but also on the relative location of the train ahead, while fixed block signals can only indicate stop or go. What passes for speed control in a fixed block system is a series of signals that only clear if a train approaches within allowable speed. And allowable speed is predefined, generally with no more than two distinct options (perhaps one general speed limit for all trains plus perhaps another more restrictive speed limit for trains closing in on their leaders).

Andrew

Since the line was extended from 6th Ave to 8th Avenue in 1931.

Perhaps my question wasn’t clear. You say that the terminal is constraining service to 24 tph. But the MTA says that power is constraining service to 20 tph. If we want more capacity on the line, the first order of business is to upgrade the power system, since that will allow an increase to 22 tph (and, presumably with further investment, to 24 tph). Improving the terminal won’t change a thing right now, since the power constraint at 20 tph will still govern.

What’s the trick? The press release states it will add 2 additional trains for a 10% increase. That means an increase from 20 to 22 tph.

Correct. So why focus on a 24 tph constraint now? There’s no point in lifting a 24 tph constraint while a 20 tph constraint remains in place.

N.B. they operated 24 tph at the 8th Ave terminal in 1954.

Scheduled. Maybe operated in practice, maybe not.

Why don’t you take a stopwatch and time them.

Because I’m comparing the speed of trains on an old signal system which no longer exists to the speed of trains on the current signal system. I’m afraid I don’t have a time machine, so I can’t in 2015 time train movements in 2007.

You need to time both the entrance and exit.

I know how to time trains at terminal interlockings…

Now add up the average of each of the 4 measurements.

…but apparently you don’t, since two of those movements don’t conflict and can take place concurrently, so I want to take the larger of the two rather than add them.

Andrew

You’re telling us how much service was actually scheduled, not maximum capacity. Maximum capacity is an upper bound on scheduled service, but ridership doesn’t necessarily warrant running as much service as the signals allow.

Who exactly claims 40 tph as an achievable capacity, in practice, with CBTC? It seems like it’s one of those numbers that just floats around with no possibility source.

sbauman

“You’ve glossed over two important differences between fixed block and CBTC systems, as least as far as they exist on the subway.”

First, by its very nature, the precision on a fixed block system is quite coarse. The signal system knows whether a block is occupied, but it has no way of knowing which part of the block is occupied. To be safe, it assumes the worst case, but that costs capacity.

Correct. However, blocks can be variable size to make the precision and accuracy finer, where it is required. If headways are 90 seconds (40 tph) and trains are traveling 40 mph (60 ft/sec), then trains are 5400 feet apart. Emergency stopping distance at 45 mph and 3.0 mph/sec emergency braking rate is 500 feet. Precision between stations is not very important.

The minimum approach distance is at station entrances. Block lengths are typically 300 ft down to 100 feet approaching and within a station. This provides adequate precision and accuracy for operating with 90 second headways.

BTW, CBTC location may be precise but it’s accuracy to the train control system is what’s important. There are transmission delays that must be considered. If communications between train and train control system drops out, the message is repeated until 2 seconds have passed (NYCT spec). At that time either the train or the train control system will halt that train. Train spacing must account for this timeout. The accuracy for train location for a train going 30 mph is 90 feet. That’s essentially the length of a block approaching a station.

Second, at least on the subway system, CBTC calculates and dictates the maximum speed on a continuous scale, based not only on track geometry but also on the relative location of the train ahead, while fixed block signals can only indicate stop or go. What passes for speed control in a fixed block system is a series of signals that only clear if a train approaches within allowable speed. And allowable speed is predefined, generally with no more than two distinct options (perhaps one general speed limit for all trains plus perhaps another more restrictive speed limit for trains closing in on their leaders).

The current block system will allow a nominal 40 tph. If the system is operating properly the follower will never see a red or yellow signal aspect due to the presence of a train ahead.

CBTC might slightly improve on this. However, current MTA practice operates far below the what the block system can handle.

Paris is converting to CBTC on routes that currently operate at 33-36 tph. Their goal is to improve it to 38-40 tph. That’s a modest improvement and indicative of CBTC’s benefits.

My suggestion is to wait until the MTA operates closer to what they did in the recent past, before embarking on CBTC.

Andrew

I’m aware of this but it’s only a small percentage of signals on some lines which are causing the issue.

From http://permanent.access.gpo.gov/websites/www.ntsb.gov/publictn/1996/RAR9603.pdf#page=20 : “Before the Williamsburg Bridge accident, the NYCT had recognized that areas in its signal system did not provide the sufficient braking distance and had contracted two companies to determine the scope of the problem. Toronto Transit Consultants noted in a study done in 1993 that older areas of the signal system did not comply with the NYCT’s design standards. The NYCT addressed the deficiency in its signal system by contracting an engineering firm, Parsons Brinkerhoff, to perform a more detailed examination of sites on the NYCT system. Parsons Brinkerhoff examined 8,257 mainline signals and other signals governing mainline train movements. In the first phase of its signal analysis, Parsons Brinkerhoff found that 51 percent of the signals between stations had no margin of safety based on the braking capability of cars before the NYCT began modifying its vehicles. The NYCT then asked Parsons Brinkerhoff to review the signal safety margins based on modified car performance and the new 1995 braking standard. The contractor completed its analysis of a section of the Queens Line and found that of the 276 signals between stations, 209 had no margin of safety based on the pre-1995 braking and acceleration tests and that all had some margin of safety based on modified car performance and the 1995 braking standard.”

Small percentage? If only. This was a serious problem, and it needed to be seriously addressed.

My source for 7.5 more trains an hour is the RPA report I linked to in m y sixth graf.

The RPA report is 72 pages long. You’re going to have to be a bit more specific than that if you want me to find it. (Searching for “7.5” produced nothing of interest, except incidentally for a table showing six subway lines with excess track capacity.)

Perhaps my estimate of a one-third increase in capacity from system-wide CBTC overstated the case. At least I’ve taken a stab at it.

By “stab” you mean “wild guess”? Sure, I can make wild guesses too – what conclusion would you like me to reach.

I’m convinced that unless we can “concretize” the value of funding this and future MTA capital plans, we’re going to end up with precious little.

The first and foremost reason to install a new signal system is that the old signal system has long exceeded its useful life. Increased capacity is certainly a nice side effect, but it’s going to have a much smaller impact than you’re envisioning here.

If you fight for capital funding by promising much more frequent service, you’ll then lose whatever support you have as soon as the public sees only slightly more frequent service and only on some lines.

And even with all the funding in the world, systemwide CBTC is going to take quite some time, because there are only so many simultaneous service outages that the system can tolerate.

Andrew

The primary issue here is that this is only a problem when/if a T/O runs a red light.

Well, yes, that’s why stop arms exist in the first place – to prevent collisions even when the T/O makes a mistake. They’re a fundamental component of the signal system.

A signal system is designed specifically to provide certain protections. If it’s found that for whatever reason it no longer provides those protections, it is no longer serving its purpose, and it needs to be redesigned in order to provide those protections once again. This isn’t optional.

Andrew

My point exactly.

Andrew

The TA actually operated 24 tph, as per the insert in their first annual report.

I don’t have an explanation for the 32 tph capacity, other than they were assuming short turning half the trains at 6th Ave.

Another possibility is that the numbers given weren’t actually achievable in practice. There’s a lot in that insert that I find hard to believe.

My timi ng studies showed that 24 tph was the capacity for 8th Ave.

Even if correct, that’s not relevant as long as power constraints hold the line back to 20 or 22.

Joe R.

My educated guess is that 32 tph was the theoretical limit of the signaling system. As I and several others mentioned, terminal capacity is the main thing which constrains train frequency on the subway.

Joe R.

My beef here is not with what the MTA initially did, but rather with it being 19 years later, and we still have what should have been quick, temporary fixes in place. The MTA should have fast-tracked fixing the signaling system to eliminate the problem. The best solution would have been adding another block between the clear and stop aspects. Based on my quick calculations, this wouldn’t have affected capacity. If we assume the signaling system now has a nominal theoretical capacity of 40 tph, we have 90 seconds between trains. Now add in another block. On average blocks are 800 feet. I’ll even allow that the train will traverse this extra block at only 15 mph. That will add 36 seconds to the time between trains, bringing it up to 126 seconds, or ~28 tph rounded down to the nearest integer. In a practical sense, the entire system is limited to less than that by terminal capacity. In practice then, there would be no capacity reduction. The beauty of this solution is that it wouldn’t have required moving signals or other expensive modifications. It probably could have been done systemwide in under 5 years. With the extra block, essentially an extra 800 feet to stop, trains easily could have been going 55 to 60 mph systemwide, at least where the runs between stations were long enough to reach those speeds.

The MTA probably decided not to modify the signaling system because it was overly optimistic about CBTC. They figured why put money into an antiquated system which we’re probably going to rip out within one or two decades. When they saw this wasn’t going to happen, they should have implemented a system-wide signal modification.

sbauman

If we want more capacity on the line, the first order of business is to upgrade the power system,

It was the MTA that decided to first install CBTC before upgrading the power system. CBTC is installed and running with only 20 tph peak hour. The MTA claims upgrading the power system with CBTC installed will allow them to operate 22 tph peak hour. Had they not installed CBTC and upgraded the power system, they would be able to operate 24 tph as they had in the past.

why focus on a 24 tph constraint now?

Suppose patronage on the 14th St line continues to grow. Will 24 tph be sufficient? This is one of the few lines that is operating close to its 1954 peak service levels. Adding more trains isn’t an option, if the terminal capacity limits service level capacity.

I’m comparing the speed of trains on an old signal system which no longer exists to the speed of trains on the current signal system. I’m afraid I don’t have a time machine, so I can’t in 2015 time train movements in 2007.

CBTC has not changed the trains’ operating characteristics nor the rule restrictions for speed on the switches or approaching the bumper block. It’s the train’s operating characteristics, the rule book and the station geometry that determine terminal capacity. These have not changed.

I did measure the times with a stopwatch before 2007. My measurements were consistent with 24 tph operation. One could also make the calculation given the train speed through the interlocking and service braking rates to come up with terminal capacity. This exercise would also result in 24 tph.

since two of those movements don’t conflict and can take place concurrently

Such operation would result in non-uniform headways. This wouldn’t a problem, if there were not any loading problems. There are crowding problems, which is why service level constraints are being discussed. Non-uniform headways are difficult to impossible to maintain, if there is crowding. Therefore, it is wise to calculate terminal capacity for uniform headways.

ahwr

Is 24 tph the terminal constraint?
I’ve seen 26 tph quoted with power upgrades.

Note in the second document (page 9) the MTA also says the old signal system was limited to 20 tph, reduced to 17 tph during construction of signal upgrades. What changed after 1954 to cut the capacity from the 24 tph they ran, with a projected capacity of 32 tph according to your link, to 20 tph according to the MTA?

Was there a new rule at some point that slowed trains to avoid any incidents, which had the effect of lowering capacity? Maybe one that isn’t necessary for an automated train? So that a new signal system that allows for an automated train to enter the terminal could increase terminal capacity?

NYCT also plans to eventually improve 8 th Avenue terminal throughput by installing an Automat ic Train Operation (ATO) system. Right now the terminal?s signaling is set up to have trains enter the station very slowly, since the tunnel ends at a wall at the west end of the station. ATO will allow L trains to automatically enter the station faster at a preset speed, thus improving line capacity. Train operators entering an ATO area are not, strictly speaking, controlling the train?s maximum speed, although they retain the ability to slow or stop the train. Instead, they are required to punch a but ton at regular intervals to acknowledge that they are still lucid and capable of taking control of the train if needed. At the time this report was being written, undisclosed health and safety aspects of this plan were a source of disagreement between NYC T and the unions which operate the transit system.

My understanding of signal systems doesn’t come from press releases. If Siemens and the MTA get it right, good for them.

Correct. However, blocks can be variable size to make the precision and accuracy finer, where it is required. If headways are 90 seconds (40 tph) and trains are traveling 40 mph (60 ft/sec), then trains are 5400 feet apart. Emergency stopping distance at 45 mph and 3.0 mph/sec emergency braking rate is 500 feet. Precision between stations is not very important.
The minimum approach distance is at station entrances. Block lengths are typically 300 ft down to 100 feet approaching and within a station. This provides adequate precision and accuracy for operating with 90 second headways.

That’s fantastic whenever service is running perfectly smoothly. Unfortunately, in real life, stuff happens, every single day, and theoretical capacity isn’t of much help when real life interferes. What happens when, say, there’s a sick passenger on a train in a station, and several trains stack up behind it? Wayside signal blocks may be closely spaced near the station but they’re much farther apart a few trainlengths back, especially where typical speeds are fast.

The current block system will allow a nominal 40 tph. If the system is operating properly the follower will never see a red or yellow signal aspect due to the presence of a train ahead.
CBTC might slightly improve on this. However, current MTA practice operates far below the what the block system can handle.

Yet every day I’m on trains that encounter red signals. Unfortunately, I live in the real world.

Paris is converting to CBTC on routes that currently operate at 33-36 tph. Their goal is to improve it to 38-40 tph. That’s a modest improvement and indicative of CBTC’s benefits.

Agreed. One of my points here has been that expecting CBTC to lead to huge capacity increases will only result in disappointment.

My suggestion is to wait until the MTA operates closer to what they did in the recent past, before embarking on CBTC.

I should wait for the MTA to operate a peak of 12 tph? No, thanks, I’ll take 20.

Andrew

It was the MTA that decided to first install CBTC before upgrading the power system.

Yes, because increasing capacity was not the objective in installing CBTC on the Canarsie line. In fact, one of the reasons the Canarsie line was selected for the pilot CBTC installation is that ridership was low.

CBTC is installed and running with only 20 tph peak hour. The MTA claims upgrading the power system with CBTC installed will allow them to operate 22 tph peak hour.

26 tph, but who’s counting? (22 is what the currently planned power upgrades will yield.)

Had they not installed CBTC and upgraded the power system, they would be able to operate 24 tph as they had in the past.

As I’ve said, I have difficulty believing that they actually operated 24 tph on a regular basis. But in any case, ridership at the time the Canarsie line was selected for CBTC required only 12 tph.

Suppose patronage on the 14th St line continues to grow. Will 24 tph be sufficient?

If even 22 tph isn’t sufficient, the power system will need to be further upgraded before anything is done with the signals or terminal.

CBTC has not changed the trains’ operating characteristics nor the rule restrictions for speed on the switches or approaching the bumper block.

Of course it has. Trains operate toward much faster toward the bumper block now than before CBTC.

It’s the train’s operating characteristics, the rule book and the station geometry that determine terminal capacity. These have not changed.

And the speed restrictions enforced by the signal system, which certainly have changed, a lot. (Remember what I said before about finer speed control under CBTC?)

I did measure the times with a stopwatch before 2007. My measurements were consistent with 24 tph operation.

Perhaps you should come back now that it’s 2015. Stuff has changed.

Such operation would result in non-uniform headways. This wouldn’t a problem, if there were not any loading problems. There are crowding problems, which is why service level constraints are being discussed. Non-uniform headways are difficult to impossible to maintain, if there is crowding. Therefore, it is wise to calculate terminal capacity for uniform headways.

If you’re worried about the uneven loads that result from uneven headways, hold trains at 6th Avenue to even them out. (If you’re worried about uneven loads, you may want to think twice before proposing short turns.)

Joe R.

Wayside signal blocks may be closely spaced near the station but they’re much farther apart a few trainlengths back, especially where typical speeds are fast.

Exactly, and this is one area where CBTC will make a huge improvement. When the congestion ahead clears, the backed up trains can enter the station one after the other, rather than needing to first cover a relatively large distance between trains at a restricted speed.

fdtutf

Yep, thanks for the correction.

sbauman

What happens when, say, there’s a sick passenger on a train in a station, and several trains stack up behind it? Wayside signal blocks may be closely spaced near the station but they’re much farther apart a few trainlengths back, especially where typical speeds are fast.”

The recovery question is which is faster after the train with the sick passenger begins to move: trains bunched together and proceeding at slow speed or trains spread further apart proceeding at near normal speeds but covering more ground. The answer is the latter.

“Yet every day I’m on trains that encounter red signals. Unfortunately, I live in the real world.”

The MTA is operating trains in a manner that is not consistent with maximum service level capacity.

Andrew

The recovery question is which is faster after the train with the sick passenger begins to move: trains bunched together and proceeding at slow speed or trains spread further apart proceeding at near normal speeds but covering more ground. The answer is the latter.

Except that the train trapped behind the incident train aren’t proceeding at best normal speeds. They’re stopped while the incident train is stopped, and one the incident train begins moving they start creeping forward.

And you’re ignoring the fact that, the closer the following trains can get to each other, the more people can reach their final destinations before the incident train has even begun moving.

The MTA is operating trains in a manner that is not consistent with maximum service level capacity.

The real world unfortunately is not consistent with (your conception of) maximum service level capacity.

Andrew

The problem can’t be fixed without a full redesign of the signal system from top to bottom. And a brand new signal system on one segment of line – whether based on fixed blocks or based on CBTC – takes years of expensive and highly disruptive work.

Unless you’re proposing to shut down the entire subway system for several months straight, which somehow I don’t think is feasible, there isn’t much fast-tracking to be done.

The Queens Boulevard express runs at 30 tph, and it has to achieve that even under imperfect conditions. Your proposal to reduce the theoretical capacity to 28 tph would require a 7% service reduction to be feasible in even the absolute best case, and in practice there’d be severe congestion virtually every single day if 28 tph were scheduled.

Joe R.

The Queens Boulevard express is actually slated to get CBTC after the #7, so that line will be fixed in the relatively near term.

As for fast tracking signal improvements (and other needed maintenance work) it might make sense to completely shut down an entire line or portions of it. I’ve heard it takes many multiples of time trying to run trains while doing improvements or maintenance. It may well be that what would take 2 or 3 years trying to do while keeping the line open could be done in 2 or 3 months if you just shut it down completely. Yes, it’ll be extremely disruptive for those few months but I feel it’s the lesser of two evils. The MTA could run shuttle buses on the portions of the line which were shut down. To keep the buses moving, the street they’re on could be closed to everything except buses.

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